The present disclosure is directed to a caliper arm mounting system and in particular a leaf spring construction for positioning between the caliper arm and the body of a caliper tool for obtaining borehole diameter measurements. In particular, the present apparatus is directed to a leaf spring system installed between a caliper arm and the tool body to thereby define a system which does not unreasonably extend the length of the tool body, to further define a spring system which can be either strengthened or weakened by selective addition of leaves therein, and to otherwise provide a very narrow structure when the arms are retracted and yet a structure which is able to operate in dynamic situations as the arms deflect inwardly and outwardly.
The leaf spring of the present disclosure tapers from one end to the other. One end is quite thick, being formed by a stack of leaves which register at the end. A fastening device is used to fasten that end of the leaf spring system against the elongate body which supports the arms; the opposite end is relatively thin, this resulting from fabrication of the spring system from multiple leaf springs. They are selected or sized so that the spring force is controlled. In addition to that, the leaf springs are constructed so that, in conjunction with the fastening device, they are parallel to the elongate body supporting the caliper arms. This parallel position enables nesting or recessing of the leaf spring in an energized state sandwiched between the body and the retracted caliper arm. On the other hand, the arm extension can be accomplished quite readily by spring power when the retracting force is removed through a pivotal link mechanism actuated by a motor unit. This enables the tip of the deflected caliper arm to ride against the wall of the borehole and thereby obtain measurements of borehole diameter. In ordinary application, two such arms are deployed opposite one another into contact with the surrounding borehole and thereby provide caliper measurements.
The present apparatus is summarized as an improved caliper arm mounting system which provides a type of leaf spring operatively connected between caliper arms and an elongate body which makes up the caliper tool. For a given arm, the arm is supported at its upper end by mounting on a pivot point and has a bell crank appended thereto to the connected measuring device. The arm is mounted so that it can retract into a flush position adjacent an elongate tubular body. Captured between the arm and the body is an elongate leaf spring which, when retracted, is parallel to the adjacent arm and adjacent body. The arm is positioned so that a connective link pivotally joins to the arm at one end of the leaf spring. The opposite end of the leaf spring is clamped to and parallel with the body and is recessed, so to speak, for alignment with the arm and leaf spring. Multiple independently operated arms are incorporated on the device.